1. Field of the Invention
The present invention relates to a cleaning system using a supercritical fluid as a solvent, and more particularly to the extraction of contaminants from articles by a cleaning process incorporating a pressure swing absorption of the contaminants in the solvent.
2. Description of the Related Art
Conventional solvent-aided cleaning processes for cleaning sensitive substrates such as fabrics or delicate electronic components have generally used dry cleaning solvents such as perchloroethylene. Due to concerns of air pollution, potential ozone depletion, occupational health and safety, and waste disposal, conventional dry cleaning solvents are being replaced with other less hazardous cleaning fluids. For these reasons, the eventual replacement of petroleum based solvents and chlorinated hydrocarbons as solvents would be desirable.
The use of a supercritical fluid or fluid mixture is being investigated as an alternative to conventional dry cleaning solvents. A supercritical fluid is a fluid which is capable of being compressed and heated to a state that exhibits high relative density and solvency compared to a gas under normal conditions while maintaining a low viscosity and surface tension. These properties make supercritical fluids desirable for use as solvents in cleaning processes. In particular, supercritical carbon dioxide has been used in garment cleaning processes to remove contaminants from garments.
One such cleaning system using supercritical carbon dioxide for cleaning of fabrics is disclosed in U.S. Pat. No. 5,267,455. In that system the cleaning is accomplished by agitation of the clothing within a pressurized vessel containing carbon dioxide in a supercritical state. The carbon dioxide is then drained, vaporized and then condensed to remove the contaminants which have been removed from the fabric. The carbon dioxide may then be reused in the cleaning system. Although the supercritical carbon dioxide in the system of U.S. Pat. No. 5,267,455 will remove many soluble contaminants such as oils and fats, it would be desirable to also remove particulate material which does not dissolve in the supercritical carbon dioxide.